The development of solid state light sources, including but not limited to light emitting diodes (LEDs), organic LEDs (OLEDs), polymer LEDs (PLEDs), and the like, has led to use of such devices in various lighting fixtures. In general, an LED is a current driven device, i.e. the brightness of the light output of an LED may be directly related to the current supplied to the LED. However, the current through an LED should be limited to a design maximum to avoid over-current damage or failure of the LED. Typically, single LED light sources operate at only 2 to 4 volts and therefore require a low voltage power supply to power them. Furthermore, the current through the LED is strongly dependent on the applied voltage and also on the temperature of the LED. For this reason, LED light sources are powered by a circuit which transforms the main voltage to a level useable by the LED light source, and also controls the current. An additional function of the circuit is to condition the current drawn from the mains supply to present the mains with a high power factor load having low harmonic distortion.
In general, it may be desirable to operate multiple LEDs in order to achieve a higher total light output level. In this case, strings of LEDs may be connected in series and powered by a circuit that is able to supply the voltage needed and maintain the desired current level. Such a circuit is typically a complex piece of electronic equipment with a number of components, including multiple inductors, power transistors, large electrolytic capacitors, and integrated circuits.